1. Field of the Invention
The present invention relates to a plasma display panel (PDP) of surface discharge structure.
2. Description of Related Art
PDPs are now attracting much attention as display devices for high definition TV. For higher definition and up-sizing of screens of the PDPs, reduction of power consumption is one of the most significant challenges.
AC-driven PDPs of surface discharge type are now commercially available as color display devices. Here, the surface discharge type means a type in which pairs of first and second main electrodes are arranged in parallel on an inner surface of one of a pair of substrates, and the first and the second main electrodes serve as positive electrodes and as negative electrodes alternately in an AC drive for sustaining a light emission state by use of wall charge. In the surface discharge PDPs, fluorescent layers for color display can be provided on a substrate opposed to the substrate on which the main electrode pairs are placed, and thereby it is possible to prevent the fluorescent layers from being deteriorated by ion impact at electric discharges and increase the life of the devices. A PDP having the fluorescent layers on a rear substrate is called a "reflection type," and the one having the fluorescent layers on a front substrate is called a "projection type." The reflection type, in which a front-side surface of the fluorescent layers emit light, is superior in luminous efficiency.
Conventionally, the main electrodes are formed in the shape of linear belts of constant width extending in a direction of rows (in a direction of display lines) within a display region. The main electrodes are usually spaced in such a manner that the space between adjacent main electrode pairs (an inverse slit width) is sufficiently larger than the space between main electrodes that make a pair (a slit width), for the purpose of preventing discharge coupling between adjacent rows. However, it is also possible to adopt a configuration in which the main electrodes are regularly spaced and each main electrode makes pairs with main electrodes adjacent on either side. Additionally, the main electrode of the reflection type is comprised of an electrically conductive transparent film and a metal film for reducing line resistance.
In the above-described surface discharge PDPs, the slit width which is a surface discharge gap and the width of the main electrodes determine a driving voltage margin. Here, the driving voltage margin means a range of driving voltages which allows stable display to be realized by use of a memory function of a dielectric, and is a difference between a firing voltage Vf and a sustain voltage Vs for sustaining electric discharges. A memory coefficient .alpha..sub.M representative of the magnitude of the memory function is defined by the following formula: EQU .alpha..sub.M =(Vf-Vs)/(Vf/2)
A larger memory coefficient .alpha..sub.M brings greater stability and easier driving. Therefore, in designing a PDP, it is desirable to adopt as low a firing voltage Vf as possible for realizing drive at lower voltages and also to increase the memory coefficient by reducing the sustain voltage Vs.
Once dimensional conditions of the main electrodes and the driving voltage are determined, the magnitude of discharge current is uniquely determined. The magnitude of discharge current can be controlled by adjusting the driving voltage within the driving voltage margin. However, since the adjustment range of the driving voltage becomes narrower with a deterioration with age, a sufficient control is practically impossible.
A larger discharge current lead to a higher luminance. At the same time, however, the increase of luminance becomes slow in consequence of ultra violet light absorption by a discharge current. As a result, the luminous efficiency (ratio of luminance to power consumption) declines. In addition, since a larger discharge current results in a larger damage to inner surfaces owing to ion impact, the discharge current must be reduced as low as possible in the viewpoint of the life. To sum up, it is impossible to set the optimum driving voltage range and the optimum discharge current independently of each other in the conventional PDPs. For determining cell structure and conditions of the discharge gas, a well-balanced drive voltage margin and discharge current must be set within a proper range through trial and error.